Automatic telephone system



June 17, 1930. R. F. GouLD AUTOMATIC TELEPHONE SYSTEM Filed Dec. 3, 1928 LNX kiwi miotlmqwh l o V o se Im-m?- E n F Enum NFOMJWW Patented June 17, 1930 UNITED STATES PATENT OFFICEA ROY F. GOULD, OF CHICAGO, ILLINOIS, ASSIGNOR TO RESERVE HOLDING COMPANY, OF KANSAS CITY, MISSOURI, A CORPORATION OF DELAWARE AUTOMATIC TELEPHONE SYSTEM Application filed December 3, 1928.

The present invention relates to automatic telephone systems in general, but is concerned more particularly with automatic telephone systems wherein trunk lines extend from a main exchange to a private branch exchange.

The invention disclosed herein is a direct improvement on the corresponding arrangement in the joint application of Schomaker and Gould, Serial No. 273,469, filed April 28,

The Schomaker and Gould application discloses a branch exchange wherein the interconnection of lines and trunk lines is accomplished by the individual line switches in which the respective lines and trunk lines terminate and under the control of a connector switch common to all of the lines and trunk lines, being known as a by-pass system.

In the Schomaker and Gould disclosure,

care of night service, and it is the object of this invention to incorporate standard night service in the system developed by Schom'alrer and Gould. In order to do this, it was found necessary to develop a new trunk circuit for use in the branch exchange in connection with the main-to-,branch trunk line. This new trunk circuit, while similar in many respects to the trunk circuit disclosed in Fig. l of the Schomaker and Gould application above referred to, differs in several important respects which may be understood after further perusal of the specification. In a trunk circuit of the type referred to herein, arrangements r must be made for momentarily supplying a local ground potential to the branch-to-main trunk line when the trunk line is seized at the branch exchange and so as to operate the line switch in which the trunk line terminates in the main exchange, the ground potential being normally removed from the trunk line at the line switch of the main exchange for reasons set forth in the said application. The provision of circuit arrangements Jfor making this ground connection on a call outgoing fromv the branch exchange to the main exchange and for removing it on an incoming call so as to give a clear talking circuit renders the usual arrangement for night service no special arrangement was made for takingy Serial No. 323,326.

unfit for use with the trunk circuit in the application hereinbefore referred to.

In addition to providing for night service, the new and improved trunk circuit disclosed herein is simpler in its circuit details and is more reliable in operation.

Referring now to the accompanying drawing comprising a single sheet, this drawing shows a sufficient amount of equipment in a telephone system embodying the features of the invention to enable the invention to be understood.

More in particular, this drawing shows the trunk line TL extending between the main exchange, part of whose equipment is shown on the left and a branch exchange, part of whose equipment is shown on the right. In the main exchange, the trunk line TL terminates in the individual line switch LS which has access to 'a plurality of selectors, one o f which is the one shown in part above the line switch. In the branch exchange, the trunk line terminates in the trunk circuit TG. Below the trunk circuit TC there is indicated certain equipment including keys and lamps located at the switchboard of the attendant and individual to the trunk circuit T C. The remaining part of the attendants switchboard is shown in Fig. l of the drawings in the Schomaker and Gould application hereinbefore referred to.

The conductors extending to the right from the trunk circuit TC and numbered 125-129, respectively, correspond, respectively, to the similarly numbered conductors shown in Fig. l of the Schomaker and Gould drawings and they extend to apparatus shown in the remaining portion of the said drawings. It may be pointed out at this time that corresponding parts in the present drawings and in the Schomaker and Gould drawings have been indicated by the same reference characters and in the same way so that a comparison may readily be made between the two.

@all from the 'main exchange to the branch exc/Lange In order that the inventionv be understood best, a detailed description of the operation of the apparatus shown will now be given. It

will first be described how a call is made from the main exchange to the branch exchange, for which purpose it will be assumed that the trunk line TL is seized in the main exchange by a main-exchange connector and over the soecalled normal conductors 107, 108, and 109. Ground potential is applied to the private normal conductor 108 when the seizure is made and the combined switching and cutoff relay 102 of the line switch LS operates and disconnects line relay 101 at the upper armature spring of the relay. Relay 102 does not completely operate owing to the usual mechanical interlocking arrangement between the l'armature thereof and the armature of the non-operated line relay 101, for which reason the wipers 104-106 are not connected up at this time. Vhen the connector seizes the trunk line TL, it makes a ground connection to the lower conductor 107 and it makes a connection from thefungrounded pole of the exchange battery to the upper conductor 109. By ymeans of the usual ringing apparatus in the main exchange, ringing current is periodically superimposed on the direct current which flows over the trunk line as a result of the battery and ground connections above pointed out.

In the branch exchange, relay 111, which is bridged across the conductors of the trunk line TL through the resistance 110 and the lower contacts of relays 120 and 115 now operates due to the direct current flowing over l they trunk line TL and closes a circuit for the slow-acting relay 113. Relay 113 operates and places ground on conductor 127, rendering the branch-exchange end of the trunk line TL busy to the connector in the branch exchange and lighting the busy lamp at the attendants switchboard.

When the first application of ringing current is made to the trunk line TL, the ringup relay 112,'whose lowerwinding is also bridged across the conductors of the trunk lineTL operates and closes a locking circuit for its upper winding at its upper contacts through contacts of relays 113 and 115. The

bridge in which the lower winding of relay 112 included, it may be pointed out, in-

cludes'the associated condenser, the lowerV contacts of relay 112, and contacts of relay 115. As a further result of the operation of y relay 112, it closes a circuit for the call lamp at its middle lower armature and at its inner lower armature 1t closes a circuit for the cutf through relay 1-16 which thereupon operates series with relay 111, limiting the direct current flow.

When the attendant notes the lighted condition of the call lamp, she removes her receiver at her telephone (not shown) and momentarily operates the connect key shown y in the lower left hand corner of the drawing, closing a circuit from the grounded conductor 136 for the lower winding of relay 117. Relay 117 operates and locks itself to the locking conductor 137 at its inner upper contacts by way of contacts of release relay 120. At its upper and lower armatures, relay 117 connects the operators common head set conductors 130 and 131 to the conductors of the trunk line TL. The connection to the upper conductor is by way of series relay 114,

and the connection to the lower conductor is by way of contacts ofthe operated relay 116.` Relay 114 now operates over conductors 130 and 131 and closes a circuit for release relayk 115, which relay thereupon operates and makes a multiple ground connection on release trunk conductor 127 at its upper armature; completes the locking circuit of relay 116 at its inner lower armature; removes relay 111 and resistance 110 from in bridge ofthe incoming conductors at its lower armature;V

and at its inner upper armature it opens the locking circuit of ring-up relay 112, whereupon relay 112 falls back and puts out the call lamp. The lower windingof relay 112 is not rebridged across the incoming conductors owing to the fact that the lower armature of relay 115 is now in operated condi!y tion. Relay 113 falls back responsive tothe deenergization of relay 111 when it is disconnected and the condition of the circuits` now is that relays 114-118 are operated while the remaining relays are in the position shown in the drawings.

As a result of the increased current flow over the trunk line TL through the low resistance relay 114 and over conductors 130 nected from the left hand side of the trunkV circuit TC.

The operator now converses with the calling subscriber and ascertains the desired number, after which she throws her usual dialling-in key, extending ground potential by way of conductor 132 to the lineswitchoperating conductor by way of contacts of relays 118 and 119. This results in the operation of the line switch (not shown) in which thel conductors 125, 126 128, 129 terminate. The operator now proceeds to dial the two digits in the desired number whereupon the connection is set up to the called line in the manner described in the hereinbefore-mentioned Schomaker and Gould application.

After having dialled the complete number, the operator restores her dialling-in key so that the two subscribers may converse with each other through the operators common equipment by way ot conductors 130 and 131, and 133 Vand 134. After listening in long enough to make sure that the right party has answered, the operator restores her receiver whereupon the holding ground potential is removed from conductor 137, permitting relay 117 to fall back and rejoin the two sections o'f the trunk circuit at the normally closed contacts controlled by armatures 121 and 124. The conductors 130, 181, 133, and 134 are now disconnected from the trunk. Relay 118 does not restore when its initial circuit is opened at the inner lower contacts of relay 117 due to the locking circuit of the relay through its own inner lower contacts and those of relay 120. Relay 118 having been operated, the restoration of relay 117 results in relay 111 being bridged across the conductors of the trunk line independent or the high vresistance 110 and through contacts of relays 116, 117, and 118. Relay 111 reoperates from the current supplied from the main exchange. The operation of relays 111 and 113 is without particular utility at this time. Relay 114 remains operated, after relay 117 falls back, through the called telephone.

Vhen the conversation is terminated, the two subscribersreplace their receivers. In case the main exchange subscriber hangs up first the connector in the main exchange releases, whereupon no further current is applied to the trunk line TL and relays 111, 113, and 114 fall back as a result, but relay 116 remains operated due to the tact that locking circuit is now completed through the contacts of relay 118. The supervisory lamp, the left hand one of the three lamps shown below the trunk circuit TC, now becomes lighted as a disconnect signal. lIts circuit includes the inner upper contacts ot relay 118, inner upper contacts of relay 115, and the middle upper contacts of relay 118. Upon noticing this disconnect signal, the operator operates her release key momentarily with the results to be hereinafter pointed out.

The foregoing description was based on the assumption that the connectors in the main exchange are of the type which release when the calling party hangs up. In case the connectors are of `another widely used type the connector does not release when the calling party hangs up, but is held operated as long as there is a current flow over the trunk line TL. In this case nothing happens in the trunk circuit TC until the called subscriber hangs up his receiver, whereupon. relay 114 falls back followed by the deenergization of relay 115, whereupon the above traced circuit for the supervisory lamp is closed. At this time, a multiple ground connection exists in its circuit at the inner contacts of relay 113.

Relay 111, being bridged across the trunk line TL independent ot' resistance 110, the current flow over the trunk line through the relay is sutiicient to maintain answered supervision in the main exchange.

In either case, the operator restores her release key momentarily, when she receives the disconnect signal, therebyv closing a circuit or release relay 120. Upon operating, relay 120 opens the locking circuit of relay 118 at its inner lower contacts, whereupon relay 118 falls back. Relay 118 opens the lool*- ing circuit of relay 116 permitting this relay to fall back, and at its lower contacts, relay 118 opens the bridge across the trunk line through relay 11.1. The main exchange connector now releases in case it has not already done so. Relay 120 falls back when the release key is restored, and the trunk circuit TC is in the normal condition shown in the drawings.v

Call from the branch exchange to the maia @rechange Considering the handling of an outgoing call, conductor 127 is grounded by theconnector switch in the automatic exchange when the connection is extended to the trunk line anda current flow is set up over conductors 125 and 129 in series and through the call ing telephone. grounded through contacts of relays 116 and 117 with the result that relay 114 of the trunk circuit TC operates in series with line relay 101 of line switch LS and over the calling line.

ground potential to conductor 127 at its upper contacts. At its lower contacts, relay 115 disconnects relay 111 and the lower winding of relay 112 from across the outgoing conductors of the trunk line and at its inner lower contacts it prepares a circuit for the cutthrough relay 116.

At the main exchange, the line switch LS rotates its wipers 10A-106 as the result of the energization of relay 101 and by the action of magnet 108, with the result that an idle selector such as the one shown in the drawing is found whereupon relay 102 operates and extends the' connection through to the idle selector. Then this occurs, ground potential is supplied to the lower conductor of the trunk line TL from a winding of the line relay of the selector and battery potential is supplied to the upper talking conduc- Conductor 129 is normally if,

Relay 115 operates from contacts ot g relay 114 and applies the usual holding lio mitting the apparatus in the branch exchange tor of thetrunk line TL from the other winding of the line relay of the selector. The release relay of the selector is operated by the line relay to place ground potential on the release trunk conductor of the trunk line extending to the selector so as to hold the line switch LS operated and to maintain the trunk line TL guarded. VWhen the lower conductor ofthe trunk line TL is grounded through the left handy winding of the line relay of the selector, a cir,- cuit is closed through contacts of relay 116 and contacts of relay 115 for the winding of cut--through relay 116. Relay 116 operates and locks itself through the contacts of relay 115, atV the same time cutting the lower trunk conductor through and removing the ground potential therefrom.

The calling subscriber now dials the mainexchange digits in the desired number whereupon the connection is set up to the desired line in the usual manner.

When the calling subscriber replaces his receiver, relay 114 falls back and the slow acting relay 115 falls back a moment later and removes ground potential from conductors 126 and 127, freeing the truck line and perto release. Relay 116 falls back when its circuit is opened at the'inner lower contacts of relay 115.

Handling night connections During the night, and at other times when the attendant is not at her switchboard, it is desirable to have arrangements made sothat calls incoming to the branch exchange can be 'handled at one of the regular telephones, sometimes the telephone at the desk ofV a night watchman. For night service, the directory listing is usually made so that a different number is called and the trunk line TL is multipled to a different point in the connector banks so that a non-rotary action of the connectors is obtained when the night number is called. Vhat is meant by this is that, in case the branch exchange number is vcalled during the day and by the regular daytime number, the connector making the call tests the trunk lines one after the other and takes any idle one, giving back a busy signal only in case they are all busy. During the night it is not desired that this happen, so one of the trunks, the one used for night service, is assigned a different numberfor night calls. The'telephone which is to be used for night service is shown in the upper right hand part of the drawing and the connection between this telephone and the regular automatic switchboard is made through normally closed contacts of the night key. When the operator leaves the attendants board at night, she throws the night key, thereby disconnecting the night telephone line lfrom the automatic switchboard and connecting it instead to the conductors 125 and 129 of the trunkV circuit TC. The lower contacts of the night key dist made from another local telephone, the trunk line TL tests busy and another of the branchto-main trunk lines is used.

Vhen the receiver is lifted at Ythe vnight telephone, with the night key thrown, a loop is closed across conductors 125 and 129, whereupon the line switch LS at the main exchange operates in the hereinbefore describedv manner and relays 114 and 115 operate in the branch exchange followed by the operation of relay 116 as hereinbeforedescribed when a first selector is found by the line switch LS. The remaining part of the outgoing call lis the same as hereinbefore described, .the connection being released when the receiver is replaced at the night telephone.

On an incoming call, relay 111 and relay 118 operate as hereinbefore described and relay 112 responds to the ringing current and operates relay 116 whereupon the lower talking conductor is switched through so as to permit the incoming ringing current to pass through to the night telephone. When the subscriber at the night telephone removes his receiver to answer, the ring-cutV-off relay in the calling connector is tripped over the trunk line in the usual manner and relay 114 operates followed by the operation of relay 115. Vthen the conversation is terminated and the called subscriber and calling subscriber replace theirreceivers, the apparatus V'shown restores to its normal position.

It will be noted that in case the call is not answered at the night telephone the operated apparatus in the trunk circuit TC restores to normal when the calling connector releases the trunklineTL, as the locking circuit of relay 112 includes contacts of relay 113 which falls back when the relay 111 opens its circuit. Y

Although the main exchange is described hereinbefore as being an automatic main exchange, it will be understood that the trunk line TL and the trunk circuit TC, as well as the local exchange apparatus, will function lsatisfactorily in connection with a main exchange of the manual type, provided the circuit conditions therein are similar to those of the automatic exchange. That is, the lower conductor of the trunk circuit TC must be normally ungrounded and is to become grounded-when the operator in the main exchange makes a connection to the trunk line on an incoming call or answers a call outgoing to the main exchange from the branch exchange.

What is claimed is:

1. In a telephone system, a two way trunk line extending between a main exchange and a branch exchange and accessible in the main exchange by way of final connectors, automatic switching apparatus ,in the main exchange responsive to an initial current flow over one conducto: of said trunk line in a circuit independent of the other conductor to prepare itself for further operation over both conductors of the trunk line in series, connections in the branch exchange made to said trunk line so as to enable the said initial current flow to take place, and means in the branch exchange responsive to a seizure of said trunk line in the main exchange for removing the said connections.

2. In a telephone system, a two way trunk line extending between a main exchange and the branch exchange and accessible in the main exchange by way of final connectors, automatic switching apparatus in the main exchange responsive to an initial current flow over one conductor of said trunk line in a circuit independent of the other conductor to prepare itself for further operation over both conductors of the trunk line in series, connections in the branch exchange made to said trunk line so as to enable the said initial flow of current to take place, circuit arrangements such that a flow of current is set up over said trunk line responsive to the seizure thereof by a main exchange connector, and means in the branch exchange responsive to said current flow for joining t-he two sections of said trunk line together.

3. In a telephone system, a two way trunk line extending between a main exchange and a branch exchange and acces-sible in the main exchange by way of final connectors, one conductor of said trunk line being divided into two sections in the branch exchange, automatic switching apparatus in the main exchange responsive to an initial current flow over the undivided conductor of said trunk line to prepare itself for further operation over both conductors of the trunk line in series, connections in the branch exchange made to the branch-exchange end of the divided conductor so as to enable the said initial current flow to take place, circuit arrangements such that a flow of current is set up over said trunk line responsive to the seizure thereof by a main exchange connector, and means in the branch exchange responsive to said current flow for removing the said connections and for joining the two sections of the divided conductor together.

4. In a telephone system, a trunk line accessible to final connector switches, means responsive to a seizure of said trunk line by a connector switch for setting up a flow of direct current over said trunk line, means for making a superimposed application of ringing current on said trunk line, a relay on circuit for said ring-up relay controlled by the irst relay.

5. In a telephone system, a trunk line accessible to final connectors, means for seizing said trunk line and for making an application of ringing current thereto, a locking device on said trunk line responsive to ring ing current, and means responsive to said trunk being freed for unlocking said device.

6. In a telephone system, a trunk line extending from a switchboard to a manual switchboard, means for seizing said trunk line at the rst switchboard and for applying ringing current thereto, a locking ring-up relay at the manual switchboard responsive to said application of ringingl current, circuit connections for signalling the operator at the manual switchboard responsive to the application of ringing current, means for extinguishing said signal when the operator responds, and means responsive to said trunk line being freed at the first switchboard before the operator responds for unlocking said ring-up relay to extinguish said signal.

7. In a telephone system wherein a trunk line extends between a branch exchange and a main exchange and wherein in order to obtain outgoing service from the branch exchange to the main exchange over the trunk line it is necessary to set up a current tlow over one conductor of said trunk line and a return separate from the other conductor and wherein one conductor of said trunk line has a special connection thereto to enable the said current flow to be set up on an outgoing call, means for seizing said trunk line in the main exchange and for applying ringing current thereto, a telephone to which said trunk line may be extended for night service in the branch exchange, and means responsive to the said seizure of said trunk line in the main exchange for removing the said special connection from one conductor of said trunk line in the branch exchange so that the s-aid application of ringing current reaches the said night telephone.

In witness whereof, I hereunto subscribe my name this 30th day of November, A. D.

ROY F. GOULD.

said trunk line responsive to said flow of direct current, a ring-up relay responsive to said flow of ringing current, and a locking 

